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Mobility is a stone's potential for further movement.
A movement is an extension from or connection to a group and moves in a particular direction away from it.
An intended movement is the threat of a movement.
Connection (as in string connection, direct connection, indirect connection) as used above is a move type.
Mobility is about which stones do have outside movement potential at all, how many of a player they are and, for every stone, in which development directions it has movement potential. Haengma is about the local to global shape relation, connectivity and shape efficiency. Mobility and haengma have in common that they consider development directions and appreciate potential on the open outside.
Mobility says: Black has 14 mobile stones and 1 immobile stone: his 'mobility count' is 14 - 1 = 13. White has 0 mobile stones but 14 immobile stones: his mobility count is 0 - 14 = -14. Both players' difference of mobility counts is the 'mobility difference': This is 13 - (-14) = 27 in Black's favour.
Local haengma says: Except for the one dead stone, the stones of Black's upper wall are well connected and efficiently shaped; probably a better shape does not exist for the same number of black stones adjacent to the upper white stones. The same can be said about Black's lower wall's stones.
Global haengma says: The upper black wall has nice potential. The lower black wall, too. They are related well together by forming good territory potential. They are too close to each other though and therefore overconcentrated. On the global scale, Black should have constructed a more efficient placement of all his stones together.
RobertJasiek: Why was this very basic strategic concept not explained here until 2011? Some even suspected that I would have invented it. Of course not! It is decades (or centuries?) old.
tapir: Well, the first thing I learned after playing on intersections and alternating was that stones don't move. This concept needs some clarification it seems.
RobertJasiek: It is superfluous to add confusion about multiple meanings of the same word. Since you have just added it, let me remove the meaning of physically running stones. Stones and groups don't run or move physically over the board - they run or move figuratively. And since you apparently need, I will create a movement page. Then you can appreciate also that fundamental better.
tapir: It is getting ridiculous. You will soon add a page "A stone, a term defined by Robert Jasiek at p.206 of ..." If mobility is just the common term as in not enclosed, space for an extension etc. - do we need a page? Or do you have something special in mind, as in solid connection?
RobertJasiek: What is ridiculous here is your resistance against learning more on the game, here in the form of terms you didn't know as terms yet. Haven't you noticed yet that go players are often very efficient in their terminology? They choose words that almost have an identity to their non-go meanings. We see this for 'connection', for 'stone' and for 'mobility'. You don't want to forget about connections, do you? Why then do you want to forget about mobility? Both are just common terms, so, according to your intention, remove all their descriptions? The opposite is the right approach: From descriptions we learn. From missing descriptions we don't learn. From meta-discussions about the value of describing things at all, we waste time that we could better use to describe further other things.
If you actually understood my explanations of mobility and movement (read them again!), then you would not confuse it with space. Space is something surrounded. Mobility is something coming from stones and having impact on space. There is the sun, the light and the space. Quite like there is the stone, its mobility and the space. Sun and light are not the same; stone and mobility are not the same. Light and space are not the same; mobility and space and not the same. Light and mobility travel through space and in directions.
Fundamentals - do you recall what Kageyama says? "What turned me from amateur to professional was getting a really firm grip of the fundamentals." The strategic concept Mobility is as fundamental and important as the strategic concept Connection. It just happens that until recently literature has so far neglected to explain mobility even more thoroughly than connection. With decades of delay, we imported a related concept (Haengma). Before nobody in Europe knew what that was. The current situation about Mobility is as bad as it was for Haengma. Hardly anybody knows it and those that don't yet put all their energy into denying having to learn it. "Fundamentals are beneath me!" the amateur would say according to Kageyama, describing their greatest failure accurately. You have just recently learned the importance of reading? You still have to learn the importance of fundamental go terms and their underlying concepts!
JoelR: My first thought when seeing the title of the page was "You mean haengma. Why didn't you say haengma?" I now see that you say mobility is related to haengma. Can you explain what is different about what you mean by mobility?
tapir: Obviously you have sth. special in mind when saying mobility as for you mobility is sth. countable etc. This wasn't clear in the original single line article, my comment was added to induce you to write a little more. No need to add polemics against my person. I am happy with this page for now, but I am pretty sure the interpretation given with mobility count and difference is originally yours and deserves to be mentioned as such in an index of terms coined by you.
John F. The Japanese literature on go is vast, and there are still very many things there that either have not made it to the west or (more commonly) have made it but in ramshackle form. What is called "mobility" here is one such latter case. The Japanese word would be hataraki, which normally means "work" but with extended meanings such as operation, function, efficiency, movement. It is regarded as a technical term in go (also appearing as ishi no hataraki). What Robert has done is to call it "mobility" and to "numberfy" it by adding the concepts of count and difference. He has not invented the underlying concept (nor has he claimed to, I think).
However, a fairly common usage in Japanese relates to groups starting to "move" (ugoku). This has nothing to do with mobility as defined here, and it is a strategic (non-joseki) idea that is not covered by RJ - at least not explicitly. Given this usage, the choice of "mobility" as the English term may be slightly unfortunate. I'm happy enough with it but I can see that others may have a different register, in which case pointing up the overlap seems fair enough in a reference
RobertJasiek: Just for the reference, I have not called it mobility but found used in English literature "mobility" and "mobile". - Surely there are more variations of usage of mobility and its perception and so a broader or more detailed treatment would be welcome. With the definition, I have only given a start. (And invented the numbers.)
tapir: I insist that "numberfying" a concept is a major change. There is a huge difference (in perception, comparability) between a hot summer day and 32°C - e.g. you won't find water of the temperature of a hot summer day because water and summer days are not comparable without turning the concept into a measure.
Also, I find it rather unfortunate that we were served a single line which in fact did not explain Robert's idea properly and only after insisting hardly, more details come along allowing to get a clue what it is about. It is also unfortunate that in that process every common word I may use is interpreted in the way Robert defined it somewhere, obviously I use it in the common meaning as in "space for an extension".
So a stone has mobility when it has the ability to develop towards the center. We are talking about a digital property a stone either has it or not, right? The mobility count is the number of stones that have it minus the stones that have not, right? But there are no half-mobile stone or very mobile stones in this conception, right? Are the following two examples correct?
RobertJasiek: Yesterday I have spent 90 minutes for providing contents but over 5 hours for discussion and meta-discussion. Enough is enough. Concerning your contents question: Mobility does not require the center but (usually) requires an outside. Not every outside is the center! Mobility WRT to mobility count is a per-stone binary feature (having or not having). In your examples, all stones are mobile because all face some outside(s). When you want to assess something else, namely to how many development directions they can move, then it is what I call number of (major) development directions (distinguishing on a 90 or 45 degrees basis).
tapir: You may not like my questions but likely I am your best reader here, I actually try to understand. That is why I ask questions, but even now this page doesn't make it clear when a stone is mobile and when not. In your above example there are 7th line white stones that are immobile, but they can move in several directions as well, when it isn't about the center why are they immobile? What is the outside when it isn't the center?
RobertJasiek: Ok, let me show the positional context I wanted to assume:
Like this, the bottom white stones also face an outside and we get a different mobility count for White: 7 - 7 = 0. The mobility difference is 13 - 0 = 13 then.
tapir: But why are the Black stones mobile here, isn't the area between them pretty much territory = inside?
RobertJasiek: That happens, when one spends too litte time on constructing examples. Let me provide an example fitting my original intention better: